In a wireless network comprising a plurality of access nodes via which a user device may access the network, it may be desirable to offer support for mobility of the user device, for example, to manage the user device moving from a one cell of the network to another cell, or where changing radio conditions, for example, make it necessary for the user device to handover to a new serving node to maintain connectivity.
Types of network currently under development are intended to permit broadband wireless access, such as networks in accordance with IEEE 802.16 standards, also sometimes referred to as WiMAX. In WiMAX, access nodes are usually referred to as base stations and the user device as a mobile subscriber station.
In WiMAX, a mobile subscriber station in communication with a serving base station, and wishing to initiate handover to another target base station, scans the frequencies of neighboring base stations until it finds a downlink signal. During scanning by the mobile subscriber station, payload data communication is interrupted to enable different frequencies to be scanned. A paper by Boone et al., “Strategies for Fast Scanning and Handovers in WiMax/802.16”, BWIA-First International Workshop on Broadband Wireless Access (IEEE ACCESSNETS 2007), Aug. 22-24, 2007, Ottawa, Ontario, Canada, proposes strategies for reducing the time required for scanning operations while performing handover between neighboring base stations in a WiMAX network. One suggested strategy is for the mobile subscriber station to build a history of handovers between base stations it has visited and for the mobile subscriber station to use this to determine which base station is the most likely neighbour target base station for a handover. The most likely candidate is scanned for first.